Phosphazene derivatives for use in the lubrication of sliding or moving parts of MRM are known in the art.
Examples of cyclophosphazene derivatives for such use are those containing at least one phosphazene cyclic group and at least one fully or partially fluorinated polyoxyalkylene chain [herein after also referred to as (per)fluoropolyether or PFPE chain] bearing one or more hydroxy groups. The phosphazene cyclic group is highly stable from the thermal standpoint and further increases the stability of the PFPE chain; without being bound to theory, it is believed that the phosphazene ring acts as a Lewis base which counteracts the catalytic effect on thermal degradation of the PFPE chain due to the Lewis acids typically present as impurities in the MRM (KANG, H. J., et al. The use of cyclic phosphazene additives to enhance the performance of the head/disk interface. Lubrication Engineering. 1999, vol. 55(3), p. 22-27.)
Certain patent documents, including US 2002183211 (AKADA TAMIO ET AL) 12 May 2002, US 2008020171 A (MATSUMURA OIL RES CORP [JP]) 24 Jan. 2008, US 2008305975 A (SEAGATE TECHNOLOGY LLC [US]) 11 Dec. 2008, WO 2007/043450 (MATSUMURA OIL RES CORP [JP]) 19 Apr. 2007 and US 2012276417 (WD MEDIA SINGAPORE PTE LTD [US]) 27 Jan. 2011 disclose lubricants for MRM containing at least one phosphazene cyclic group bearing at least one optionally substituted phenoxy group and at least one hydroxy-substituted PFPE chain.
However, it has been observed that the optionally substituted phenoxy group on the phosphazene ring might reduce the mobility of the lubricant and decrease the durability of the MRM. Thus, it would be desirable to provide PFPE phosphazene derivatives for the lubrication of MRM that do not show this drawback.
US 2012251843 (SEAGATE TECHNOLOGY LLC [US]) 10 Apr. 2012 discloses, inter alia, a composition comprising a central core comprising a cyclic group, including a cyclotriphosphazene, and six arms extending from the central core, wherein each arm comprises a PFPE or a PFPE derivative. The PFPE derivative can be a PFPE chain having one or more terminal functional groups including: —CH2OH, —OCH2CH2OH, —CH2CH(OH)CH2OH, —CH2CH(OH)CH3 and —OCH2CH2CH2OH. The PFPE derivative can also have non-terminal functional groups including —CH2CH(OH)CH2—, —CH(OH)CH(OH)CH2—, —CH2CH(OH)CH2CH(OH)CH2—, —CH(CH2OH)— and —CH(OH)CH(OH)CH2—.
US 20090318664 A (SEAGATE TECHNOLOGY LLC) 24 Dec. 2009 discloses compounds comprising a backbone comprising a PFPE chain; one or more cyclophosphazene rings attached to or incorporated into the backbone; and at least two functional groups attached either to the backbone or to the cyclophosphazene ring or both. In particular, this document refers to compounds wherein the cyclophosphazene ring comprises alkoxy or aryloxy substituents.
US 2012/0219826 (SEAGATE TECHNOLOGY LLC) discloses composition for use in lubricating thin film storage media, the composition including one or more central cores, wherein each arm comprises phenol or piperonyl.